The inductive consumer is, for example, an actuator or the like, which is used, in particular, in a transmission of a motor vehicle, for example, an automatic transmission. To operate the consumer, the consumer is supplied with electric current, and the behavior of the consumer is capable of being influenced by adjusting the current intensity. The consumer may be present, for example, in the form of a solenoid valve, in which a flow-through cross section for a fluid and, therefore, the flow-rate of the fluid through the solenoid valve, may be adjusted via the current intensity.
To control the current intensity, the consumer is connected in series to the switching device and to the current measuring unit. The switching device is used either to supply the consumer with electric current or to interrupt the current feed. This takes place using a pulse width modulation method, so that the switching device is correspondingly activated for adjusting the current intensity during a pulse width modulation period or during a plurality of successive pulse width modulation periods. The activation occurs here with a certain pulse duty factor, which indicates over which temporal portion of each pulse width modulation period the consumer is to be supplied with electric current.
At a pulse duty factor of zero, for example, no current at all is supplied to the consumer, whereas at a pulse duty factor of one, current is supplied over the entire pulse width modulation period. The pulse duty factor is normally established separately for each pulse width modulation period. Any arbitrary pulse duty factor from zero to one is, of course, selectable, so that the portion of the pulse width modulation period during which the consumer is supplied with electric current may be arbitrarily adjusted. Accordingly, the behavior of the consumer may also be arbitrarily influenced.
The current measuring unit is used to determine, in particular by measuring, the electric current actually flowing through the consumer, or the current intensity thereof. The current measuring unit in this case includes, for example, a so-called shunt resistor. Based on the voltage drop across the resistor, it is possible to deduce the current intensity of the electric current flowing through the consumer and the shunt resistor. The free-wheeling element, which is designed, for example, as a free-wheeling diode, is normally present in parallel to the consumer. The free-wheeling element is used, in particular, to protect the consumer from over-voltages, which may occur when the power supply of the inductive consumer is interrupted with the aid of the switching device, primarily as a result of self-induction. The free-wheeling element thereby prevents the occurrence of excessive voltages and, thus, potential adverse effects or damage to the inductive consumer.
Due, in particular, to the self-induction of the inductive consumer, the latter exhibits a hysteresis-like behavior, which means that an exact adjustment of the current intensity may no longer be readily carried out due to inaccuracies resulting from the hysteresis-like behavior, so that the actual current intensity of the electric current flowing through the inductive consumer may only be approximately adjusted.